The employment of magnetoresistive (MR) sensors for reading signals from media is well known. MR sensors read signals from the media by detecting a change in resistance of the sensor due to magnetic fields from the media. Many variations of MR sensors are known, such as anisotropic magnetoresistive (AMR) sensors, dual stripe magnetoresistive (DSMR) sensors, giant magnetoresistive (GMR) sensors, spin valve (SV) sensors, dual spin valve (DSV) sensors and current-perpendicular to plane (CPP) sensors such as spin-dependent tunneling (SDT) sensors.
Common to these sensors is the need to provide bias fields, both to eliminate noise and to facilitate signal readout. A known means for biasing the sensor involves forming a permanent magnet next to ends of the sensor that form part of a contiguous junction across plural sensor layers. Conductive leads may be formed on the permanent magnet layers next to the contiguous junction.
In order to form contiguous junctions, a sensor is typically deposited in layers and then sensor ends are defined by masking and ion beam milling or etching (IBE), reactive ion etching (RIE) or the like. Before the mask that protected the sensor layers during etching has been removed, bias and lead layers are deposited adjacent the ends to form junctions. Removing the mask lifts off the bias and lead materials that have been deposited on the mask, leaving the bias and lead layers on both sides of the junctions.
FIG. 1 shows a prior art sensor 20 with contiguous junctions (CJ) 22 disposed between the sensor and material that provides electrical current and magnetic bias fields to the sensor. The view in FIG. 1 is one that would be seen from a medium facing the sensor and looking through a thin diamond coating of the sensor. The sensor 20 has been formed on a major surface of a substrate 25 such as a silicon, alumina or alumina-titanium-carbide wafer.
Atop the substrate 25 a first shield layer 28 of NiFe was formed. A read gap layer 30 of alumina (Al2O3) was formed over the first shield 28, and an antiferromagnetic (AF) layer 33 was formed atop the read gap 30. Atop the AF layer 33 is a pinned ferromagnetic layer 40, a non-magnetic, electrically conducting spacer layer 42 such as copper or gold, a free ferromagnetic layer 44, and a protective cap layer 46. After these layers were deposited, a dual layer lift-off mask, not shown in this figure, was patterned atop the sensor layers. The sensor layers were then milled by rotating IBE to create the CJ 22, partially milling the read gap layer 30.
Underlayers 50 were then formed of chromium (Cr), on the exposed read gap 30 and CJ 22. Permanent magnet bias layers 52 were then formed on the underlayers 50, followed by lead layers 55. A second read gap layer 60 were formed to electrically isolate the sensor layers from a second shield 62.
It is known that a predominantly (002) Cr seed layer structure induces an in-plane (1120) in cobalt based alloys. The Cr (002) structure, however, typically requires substrate heating of over 200° C. during the deposition process, which is not compatible with wafer fabrication processes of magnetic heads.
Without substrate heating, the present inventors have observed a predominantly (110) Cr crystalline structure when Cr is deposited on glass, oxidized silicon (Si), or alumina-coated AlTiC substrates. The (110) Cr texture promotes a mostly (1011) crystalline structure in a subsequently deposited Co-based layer, for which the C-axis of cobalt is tilted out-of-plane by 28°. In addition, a substantial number of Co crystallites would have the C-axis perpendicular to the plane, which could be favorable for CJ 22 and hard bias layers that are nearly perpendicular to the sensor layers, but detrimental for CJ 22 and hard bias layers that are removed from perpendicular to the sensor layers. Moreover, the present inventors have discovered that a Cr underlayer may grow without a preferred texture, which can randomize the C-axis orientation of the adjoining Co-based layer, reducing its magnetic moment and coercivity. The present inventors have also discovered that other layers that do not adjoin the bias layers can negatively affect the crystalline structures of the bias layers, reducing the coercivity and magnetic moment of the bias layers. For example, an AF layer 33 formed of platinum-manganese (PtMn) has a strong texture that may transcend a Cr underlayer 50, denigrating the crystalline structure of the overlying bias layers 52.